Fuel cell power plants include fuel gas steam reformers which are operable to catalytically convert a fuel gas, such as natural gas or heavier hydrocarbons, into the primary constituents of hydrogen and carbon dioxide. The conversion involves passing a mixture of the fuel gas and steam through a catalytic bed which is heated to a reforming temperature which varies depending upon the fuel being reformed. Catalysts typically used are nickel catalysts which are deposited on alumina pellets. There are three types of reformers most commonly used for providing a hydrogen-rich gas stream to fuel cell power plants. These are a catalytic steam reformer, an autothermal reformer, and a catalyzed wall reformer. In addition, hydrocarbon fuels may be converted a hydrogen-rich gas stream by use of a partial oxidation reaction apparatus. A typical catalytic steam reformer will consist of a plurality of reaction tubes which are contained in a housing that is insulated for heat retention. The reaction tubes are heated by burning excess fuel gas in the housing and passing the burner gas over the reaction tubes. The reforming temperature is in the range of about 700° F. to about 1,600° F. The individual reaction tubes will typically include a central exhaust passage surrounded by an annular entry passage. The entry passage is filled with the catalyzed alumina pellets, and a fuel gas-steam manifold is operable to deliver the fuel gas-steam mixture to the bottom of each of the entry passages whereupon the fuel gas-steam mixture flows through the catalyst beds. The resultant heated mixture of mostly hydrogen and carbon dioxide gas then flows through the central exhaust passages in each tube so as to assist in heating the inner portions of each of the annular catalyst beds; and thence from the reformer for further processing and utilization. Such catalytic steam reformers are described in U.S. Pat. No. 4,098,587
A typical autothermal reformer may be a single bed or a multiple bed tubular assembly. Autothermal reformers are often used when higher operation temperatures are required for the reforming process because the fuel to be processed is more difficult to reform. In an autothermal reformer, the reaction gasses are heated by burning excess fuel within the reaction bed by adding air to the fuel and steam mixture so that the remaining fuel-steam mixture is increased to the temperature necessary for the fuel processing reaction.
Typically, wall temperatures in an autothermal reformer are in the range of about 1,400° F. to about 1,800° F. Such reformers are described in U.S. Pat. No. 4,473,543.
A third type of prior art reformers have utilized catalyzed wall passages such as described in U.S. Pat. No. 5,733,347. Such reformers are formed from a sandwich of essentially flat plates with intervening corrugated plates which form reformer gas passages and adjacent regenerator-heat exchanger passages. Each of the reformer passage plate units is disposed directly adjacent to a burner passage plate unit so that the adjacent reformer and burner passages share a common wall.
Besides the reformer devices described above, a partial oxidation reaction apparatus may also be used to produce a hydrogen-rich fuel stream. This device is typically a chamber that is fed a hydrocarbon fuel, steam and oxidant source, usually air, so that the mixture spontaneously partially oxidizes to form a hydrogen-rich mixture. Such devices, for example, are disclosed in PCT application WO 98/08771.
U.S. Pat. No. 4,451,578, granted May 29, 1984 contains a discussion of autothermal reforming assemblages, and is incorporated herein in its entirety. The autothermal reformer assembly described in the '578 patent utilizes catalyzed alumina pellets. Although autothermal reformers allow a degree of system compaction, it would be desirable to further decrease the size and weight of an autothermal reformer, and also of any tubular reformer, particularly in systems which are utilized in vehicular applications. Attempts have been made to decrease the size and weight of autothermal and other tubular reformers through the use of specially configured catalyst pellets. Such specialized pellet configurations include rings, flat pellets with holes, wagon wheel-shaped pellets, and lobed pellets, for example.
It would be desirable to provide an autothermal reformer assembly which does not require the use of specially configured catalyzed alumina pellets, and which is more compact and light weight than the prior art autothermal reformer assemblies which do utilize catalyzed alumina pellets. Such reformer assemblies would find particular utility in vehicular applications.